1. Field of the Invention
The present invention relates to an image forming apparatus such as a copier, a printer, a facsimile, and a multi-function printer, and more specifically to a configuration in which a plurality of image carriers is juxtaposed in a conveying direction of a conveyance body.
2. Description of the Related Art
In regard to an electrophotographic color image forming apparatus, various types of so-called tandem type image forming apparatuses each including a plurality of image forming portions and configured to transfer images of different colors sequentially on an intermediate transfer belt or on a recording medium held on a conveyor belt is proposed to speed up operations.
However, such tandem type image forming apparatuses have the following problem. That is, a gap or the like may occur between travels of an outer circumferential surface of a photoconductive drum and the intermediate transfer belt at a transfer position of each image forming portion variously per each color due to fluctuation of speeds of the plurality of photoconductive drums and the intermediate transfer belt caused by uneven mechanical precision or the like. Therefore, the tandem type image forming apparatuses have a possibility of causing a color registration error, i.e., a color shift of respective colors, when the images are superimposed.
Then, various configurations for suppressing such a color shift have been proposed since the past. For instance, according to one configuration, image position information provided on an intermediate transfer belt and image position information provided on a photoconductive drum are read, respectively, by information detecting portions separately provided. Then, each image forming portion is controlled such that an image formed on a first photoconductive drum located upstream in a conveying direction of the intermediate transfer belt and transferred to the intermediate transfer belt coincides with an image formed on a second photoconductive drum located downstream in the conveying direction. It is noted that a method utilizing an electrostatic latent image, a magnetic record or the like is used to form the image position information.
For instance, in configurations described in Japanese Patent Application Laid-open Nos. 2009-134264 and 2004-145077, an information detecting portion for detecting information on a photoconductive drum and an information detecting portion for detecting information on an intermediate transfer belt are separately installed. That is, the information detecting portions are mounted separately. Due to that, fluctuation of relative positions of the respective information detecting portions caused by temperature changes or the like and a difference of vibrations of the respective information detecting portions may cause an error in registering the images.